1. Field of the Invention
The invention relates to gas separation with heating or cooling means for gas, with two confined fluids in indirect contact; and also to processes for gas separation of vapors and gases, especially vapors of sulfur and its compounds. The invention also relates to a system to separate noncondensable gases from condensable gases or vapors and to equipment to accomplish this separation. In particular, the invention is for removal of hydrogen sulfide gas from geothermal steam.
2. Description of the Prior Art
Geothermal steam is produced in many parts of the world and harnessed for generation of electricity, among other useful ends. The pressurized steam contains a variety of other noncondensable gases that may include carbon dioxide, ammonia, nitrogen, hydrogen, hydrocarbons, and hydrogen sulfide. After the steam passes through a turbine for generation of electricity, it may be either condensed or discharged directly to the atmosphere. The various gases are partially or completely liberated to the atmosphere either directly from the condenser or during later processing of the condensate from the condenser. The H.sub.2 S gas so liberated is a pollutant and is undesirable in high local concentrations.
Hot geothermal brines and water are also produced for generation of electricity and other purposes. These brines and waters may also contain dissolved gases including H.sub.2 S gas. The utilization of these hot waters often involves a reduction of pressure so that part of the water flashes to steam. When this occurs, much and probably almost all of the H.sub.2 S, depending on the specific process conditions, will transfer into the steam phase. The potential pollution problems when the steam is processed then become similar to those when dry steam, as opposed to hot liquid, is produced from a geothermal well.
Air pollution problems due to the release of H.sub.2 S gas from chemical processes have been long present and recognized. This is particularly true in the petroleum and petrochemical industries. A large number of processes for H.sub.2 S removal have been developed and put into use in various commercial industries. However, none of these have been found to be particularly applicable to geothermal steam.
Several recent research efforts have attempted to remove H.sub.2 S from geothermal steam or liquid. These include absorption into copper sulfate and similar solutions, and direct oxidation by adding oxygen to a liquid, H.sub.2 S-bearing stream. No commercially acceptable process is known to have resulted from these efforts.
With respect to the abatement of H.sub.2 S emissions resulting from the use of geothermal steam, hot brines, or hot water, two specific applications of the present invention are envisioned, as described below.
When a geothermal well is drilled, whether it is in a new area or in an extension of an established well field, it is often necessary to test the well for an extended period of time. This testing generally consists of blowing steam to the atmosphere with the well bore completely open, or partially "choked" to restrict flow, and has such purposes as to estimate the size of the reservoir and the potential life of the well, as well as clean the well of loose solid matter. When testing or cleaning is satisfactorily completed, the well may be shut in until the flow from the well can be directed to a process plant. The process plant will usually not be built until several wells have been completed and tested, so that the geothermal reservoir has been proven capable of sustaining the process plant for a sufficiently long period of time to justify the expense of its construction.
During the testing of the wells, the H.sub.2 S contained in the steam is emitted directly to the atmosphere. In this mode of operation, no simple and economic means is known to recover the H.sub.2 S so as to prevent its emission to the atmosphere. One aspect of this invention is to provide such a means.
After construction of a process plant, geothermal steam from one or several wells will be directed to the plant. It is generally preferable to remove the H.sub.2 S from the steam upstream of the process plant, where the steam is still pressurized and occupies a considerably smaller volume than it would downstream of the plant, as at the exit of a turbine. Another aspect of this invention is to provide a system for removal of H.sub.2 S from geothermal steam within a process plant, preceding all or most of the plant process equipment.
The processes and devices described can also be used for the removal of various other noncondensable gases from other condensable gases and vapors differing considerably from geothermal steam. The process may also be applied downstream of other process equipment if this design configuration is preferred.